This invention relates to end effectors for robotic handlers such as might be used in materials processing, e.g. semiconductor wafer processing.
Robotic handlers are commonly used to move materials, e.g. semiconductor wafers, between different stages of a wafer fabrication process. For example, robotic handlers might be used to move the wafer, from a plasma etch station in a cluster tool to a deposition station or from a manufacturing station to a testing station. At some stages of the manufacturing process, the wafer that is delivered by the robotic handler must be in a known orientation. For example, if the stage involves a masking process, the orientation of the wafer is critical since the mask must be aligned with the previously formed patterns on the wafer. To achieve the proper alignment, the robotic handler typically moves the wafer to something referred to as a pre-aligning station. After the wafer is deposited at this station, the pre-aligner positions the wafer and rotates it to a predetermined orientation. Then, the robotic handler picks up the oriented wafer and moves it to the next processing stage.
A typical robotic handler includes an end effector and a robotic arm. The end effector is the part of the robotic handler that holds the wafer. The arm includes the mechanical mechanisms that are used to move the end effector and the wafer which it holds to the desired location.
In general, in one aspect, the invention is an apparatus for holding and orienting a wafer having an alignment feature. The apparatus includes a movable robot arm; and an end effector attached to an end of the robot arm. The end effector includes a gripping mechanism which during operation both holds the wafer and rotates it about an axis that is perpendicular to the plane of the wafer and a sensing element for detecting the alignment feature on the wafer as the gripping mechanism rotates the wafer past the sensing element.
Other embodiments of the invention include one or more of the following features. The gripping mechanism includes a first contacting member, a second contacting member, and a drive element which increases and decreases the space between the first and second contacting members in response to a control signal. The first and second contacting members are arranged to grip opposing edges of the wafer. The first contacting member includes a first roller element and the second contacting member includes second and third roller elements separated in space from each other. The gripping mechanism also includes an mechanical actuator which is coupled to and moves the first roller element towards and away from the second and third roller elements. The first roller element has a cylindrically-shaped outer surface with a circumferential groove formed therein. The first, second and third roller elements are arrayed in a common plane and have parallel axes of rotation. The gripping mechanism further includes a drive motor which rotates the first roller element.
Other embodiments also include the following additional features. The sensing element includes a light emitter and a light detector. The light emitter and the light detector are positioned to lie on opposite sides of the wafer when the wafer is being held by the gripping mechanism. The sensor senses the orientation by detecting a feature on the perimeter of the wafer as the wafer is rotated.
The invention has one or more of the following advantages. The end effector allows a user to align the wafer without transferring the wafer to a separate pre-aligner. This eliminates the loss in alignment precision that might otherwise result from transferring the wafer from the pre-aligner to the end-effector. This also tends to reduce or eliminate possible contamination to the wafer that might tend to result from the additional contact with the pre-aligner. Eliminating the wafer transfers from the robot arm to the pre-aligner and back also saves time, thus increasing processing throughput.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.